The present invention relates to a photographic cassette to manipulate and expose a light-sensitive sheet, in particular for use in a large format camera.
Cassettes of this kind have been known for a long time. They have a flat housing to insert a light-sensitive sheet and a light-proof slider, designed to be movable on the housing. The function of the slider is to open the opening in the housing or close it against the light. The opening is adjusted to the shape and size of the light-sensitive sheet and, when exposing the sheet, permits the light to enter, when the light-proof slider is moved into the open position. The housing has a supporting surface to brace the back side of the sheet, inserted in the housing, the back side is turned away from the light-sensitive layer; and there are also retaining members to reach over the edge of the light sensitive front side of the sheet, inserted in the housing. The retaining members must hold the light-sensitive sheet at the supporting surface in as planer a position as possible.
In cassettes with a plastic housing, e.g. according to the USAS PH3.26-1951 standard, the retaining members are formed by struts in the housing and are thus not movable. Therefore, a light-sensitive sheet cannot be inserted through the opening of the housing, the opening being to expose the sheet, into the housing at a right angle to the plane of the sheet or removed from the housing. Rather it is necessary to push in or take out the light-sensitive sheet through a slot at the same angle as the plane of the sheet. Consequently the loading and unloading of such cassettes is tedious and must be carried out in a dark room.
So-called ferro-cassettes, which were originally designed for the insertion of glass plates with a light-sensitive layer, are also known. These ferro-cassettes include such cassettes in which at least one part of the retaining members is movable. And for loading and unloading the cassette, the members can be moved out of their original effective positions into ineffective positions so that in principle a photographic sheet or a photographic glass plate can be inserted into the cassette or can be taken out of the cassette through the opening in the housing, the opening permitting the light to enter when exposing, in a direction perpendicular to the plane of the sheet or the glass plate, when the light-proof slider is moved into its open position. In a known embodiment of this cassette, the retaining members are designed stationary on two parts of the floor of the housing such that they are movable with respect to one another, whereas in another known embodiment the movable retaining members are movable via a double eccentric, which can be actuated externally and pivoted in the floor of the housing. Ferro-cassettes of the described type are not usable in modern large format professional cameras and are suitable only for loading flexible light-sensitive film sheets instead of rigid glass plates. In addition to this, they require for loading and unloading time-consuming, careful manipulation with respect to coordinating the movements of the light-proof slider and the movable retaining members. Therefore, operational errors and thus related damage to the photographic material, in particular due to finger prints, are possible.
In the described conventional cassettes there is a fixed distance which forms the intermediate space between the supporting surface for the back side of a light-sensitive sheet on the one hand and the retaining members, which reach over the edge of the light-sensitive layer of the sheet on the other hand. The edges of the sheet have space in the intermediate space. Since the light-sensitive sheet, which will eventually be used, can have a variable width and because in addition thereto, there must be plenty of free space in order to insert the light-sensitive sheet or for pushing the movable retaining members over the sheet, the aforementioned distance must be relatively large. Thus, according to the aforementioned USAS PH3.26-1951 standard, it is at least 0.012 inches =0.3 mm. This means that the flexible film sheet that is usually used today and which has a thickness, ranging in tolerance from 0.19 to 0.24 mm, is not always exactly planar in the cassette. Thus the clarity of the photographic image can be impaired.